1. Field of the Invention The present invention relates to subsurface well equipment and, more particularly, to a subsurface safety valve.
2. Description of the Related Art
The use of subsurface safety valves in oil and gas wells is well known. U.S. Pat. No. 4,660,646 to Blizzard, which is fully incorporated herein by reference, describes the use of a xe2x80x9cflapperxe2x80x9d type valve disposed within the well bore which is opened and closed with a flow tube, generally a cylindrical tube which moves telescopically within the well bore. The Blizzard flow tube is actuated using a piston and cylinder assembly. One of the piston or cylinder is attached to the flow tube, and when hydraulic pressure is applied to the piston, the piston moves down as does the flow tube, thereby actuating the safety valve to an open position.
It is also well known that the fluid column acting on the piston and cylinder assembly to open the subsurface safety valve applies ever greater pressure the deeper the piston and cylinder assembly is set into the earth. Therefore, the force required to lift the flow tube, and close the valve, increases accordingly. Generally, spring force and sometimes hydraulic pressure is used to lift the flow tube and close the valve. Occasionally, the piston and cylinder assembly used to lift the flow tube fails due to seal wear or other well known mechanical failure. In the case of such a mechanical failure, if the aforementioned spring is not strong enough to overcome the force applied by the fluid column, the valve will fail in the open position. A failure in the open position is generally undesirable as being unsafe, and operationally inefficient. As such, various techniques have been employed to ensure that in the event of a failure, the valve will fail in the closed position.
The present invention is directed to a subsurface safety valve that, in the event of a failure, fails in the closed position.
The present invention has been contemplated to meet the above described needs. In a broad aspect, the invention may include a subsurface safety valve for controlling a fluid flow through a well conduit comprising: a housing having a bore and disposed within an annulus defined by the space between the well conduit and the housing; a valve closure member movable between an open position and a closed position, and adapted to restrict the fluid flow through the bore when in the closed position; a flow tube moveably disposed within the housing and adapted to shift the valve closure member between its open and closed positions; a piston assembly including a piston member in sliding relationship with a cylinder, the piston member in mechanical communication with the flow tube, the piston member having a first seal, a second seal, and a third seal, each seal sealing against the cylinder, and the third seal disposed between the first and second seals; and a failsafe passageway in fluid communication with a balance pressure line and a portion of the piston member between the first and second seals. Another feature of this aspect of the present invention may be that the failsafe passageway is in fluid communication with the portion of the piston member between the first and third seals; and the piston member is in mechanical communication with the flow tube between the second and third seals. Another feature of this aspect of the present invention may be that the failsafe passageway is in fluid communication with the portion of the piston member between the second and third seals; and the piston member is in mechanical communication with the flow tube between the first and third seals. Another feature of this aspect of the present invention may be that the balance pressure line is in fluid communication with the annulus. Another feature of this aspect of the present invention may be that the balance pressure line includes a filter. Another feature of this aspect of the present invention may be that the balance pressure line is in fluid communication with a source of pressurized fluid at the earth""s surface. Another feature of this aspect of the present invention may be that the piston member is a rod piston. Another feature of this aspect of the present invention may be that the piston assembly includes a disengageable piston member. Another feature of this aspect of the present invention may be that the disengageable piston member is in mechanical communication with the piston member. Another feature of this aspect of the present invention may be that the disengageable piston member is in hydraulic communication with the piston member. Another feature of this aspect of the present invention may be that the balance pressure line is in fluid communication with the annulus. Another feature of this aspect of the present invention may be that the balance pressure line is in fluid communication with a source of pressurized fluid at the earth""s surface. Another feature of this aspect of the present invention may be that a first end of the piston member is in fluid communication with a control pressure line and a second end of the piston member is in fluid communication with the balance pressure line. Another feature of this aspect of the present invention may be that the invention may further include a spring member adapted to force the flow tube toward its first position.
In another aspect, the invention may be a subsurface safety valve for controlling a fluid flow through a well conduit comprising: a housing having a bore and disposed within an annulus defined by the space between the well conduit and the housing; a valve closure member movable between an open position and a closed position, and adapted to restrict the fluid flow through the bore when in the closed position; a flow tube moveably disposed within the housing and adapted to shift the valve closure member between its open and closed positions; and a piston assembly having a piston member and a disengageable piston member, the piston member being in fluid communication with a control pressure source and in mechanical communication with the flow tube, the disengageable piston member being adapted to cooperate with the piston member to selectively cause the flow tube to shift the valve closure member to its closed position, at least one of the piston member and disengageable member being in fluid communication with a balance pressure line, the balance pressure line being in fluid communication with the annulus. Another feature of this aspect of the present invention may be that the balance pressure line includes a filter. Another feature of this aspect of the present invention may be that the invention may further include a spring member adapted to force the flow tube toward its first position. Another feature of this aspect of the present invention may be that the piston assembly is a detachable piston assembly disposed within a cylinder and in mechanical communication with the flow tube, the piston assembly having a lower piston member and an upper piston member, one end of one of the upper and lower piston members being in fluid communication with the control pressure source, and one end of the other of the upper and lower piston members being in fluid communication with the balance pressure line. Another feature of this aspect of the present invention may be that each of the upper and lower piston members includes an internal passageway, the valve further including a piston rod having a piston rod valve member, disposed within the internal passageways of the upper and lower piston members and being detachably connected to the lower piston member. Another feature of this aspect of the present invention may be that invention may further include a first seal disposed about the upper piston member, a second seal disposed about the lower piston member, a third seal disposed about the lower piston member at a location between the first and second seals, and a failsafe passageway in fluid communication with the balance pressure line and portions of the upper and lower pistons located between the first and third seals. Another feature of this aspect of the present invention may be that the disengageable piston member is in mechanical communication with the piston member. Another feature of this aspect of the present invention may be that the disengageable piston member is in hydraulic communication with the piston member. Another feature of this aspect of the present invention may be that the piston member includes a first seal, a second seal, and a third seal, the third seal disposed between the first and second seals; and a failsafe passageway in fluid communication with a balance pressure line and a portion of the piston member between the first and second seals.
In yet another aspect, the present invention may be a subsurface safety valve for controlling a fluid flow through a well conduit comprising: a housing having a bore and disposed within an annulus defined by the space between the well conduit and the housing; a valve closure member movable between an open position and a closed position, and adapted to restrict the fluid flow through the bore when in the closed position; a flow tube moveably disposed within the housing and adapted to shift the valve closure member between its open and closed positions; and a piston assembly having a piston member and a disengageable piston member, the piston member being in fluid communication with a control pressure source and in mechanical communication with the flow tube, the disengageable piston member being adapted to cooperate with the piston member to selectively cause the flow tube to shift the valve closure member to its closed position, at least one of the piston member and disengageable member being in fluid communication with a balance pressure line, the balance pressure line being in fluid communication with a source of pressurized fluid at the earth""s surface. Another feature of this aspect of the present invention may be that the valve may further include a spring member adapted to force the flow tube toward its first position. Another feature of this aspect of the present invention may be that the piston assembly is a detachable piston assembly disposed within a cylinder and in mechanical communication with the flow tube, the piston assembly having a lower piston member and an upper piston member, one end of one of the upper and lower piston members being in fluid communication with the control pressure source, and one end of the other of the upper and lower piston members being in fluid communication with the balance pressure line. Another feature of this aspect of the present invention may be that each of the upper and lower piston members includes an internal passageway, the valve further including a piston rod having a piston rod valve member, disposed within the internal passageways of the upper and lower piston members and being detachably connected to the lower piston member. Another feature of this aspect of the present invention may be that the valve may further include a first seal disposed about the upper piston member, a second seal disposed about the lower piston member, a third seal disposed about the lower piston member at a location between the first and second seals, and a failsafe passageway in fluid communication with the balance pressure line and portions of the upper and lower pistons located between the first and third seals. Another feature of this aspect of the present invention may be that the disengageable piston member is in mechanical communication with the piston member. Another feature of this aspect of the present invention may be that the disengageable piston member is in hydraulic communication with the piston member. Another feature of this aspect of the present invention may be that the piston member includes a first seal, a second seal, and a third seal, the third seal disposed between the first and second seals; and a failsafe passageway in fluid communication with a balance pressure line and a portion of the piston member between the first and second seals.